a. The Field of the Invention
This invention relates to the art of road marking and more particularly of producing light reflecting and collimating systems designed for improving nighttime visibility of traffic regulating signs and markers such as traffic lane dividing lines and other signs formed on traffic carrying road surfaces. More specifically, this invention is concerned with light reflecting aggregates or systems adapted to be at least partially embedded in the road surface-forming and sign-forming material and comprising a combination and arrangement of spherical and part-spherical transparent, reflective and refractive elements cooperatively correlated so that the light rays emitted by a vehicle headlamps, in a direction forming a very small angle with the generally planar surface of the road, and impinging on an exposed part-spherical portion of the system, are so refracted and reflected within the system that at least some such rays are returned towards the source of light and made visible to the vehicle's driver.
B. The Prior Art
The art to which this invention appertains is a well worked one and a wide technical and patent literature exists and deals with the various aspects of the problems involved in securing an effective nighttime visibility of traffic regulating signs applied on or formed at the road surface, when the sole or principal source of light is provided by the vehicle's headlamps, that is when the signs are illuminated at a distance by "grazing" light, that consists of light rays forming the above indicated very small angle with the road surface, of one or a very few degrees. One mode for improving such nighttime visibility of traffic aids on traffic carrying surfaces has been for example described in my prior U.S. Pat. No. 3,746,425.
Other modes for reflecting a ray of light back along its own path of incidence have been proposed heretofore. For example, in the U.S. Pat. No. 3,311,441 there has been proposed a "collinear reflector" obtained by locating a short focus lens, which may be in the forms of a sphere of relatively large diameter, in front of a reflex reflecting surface made up of a plurality of glass beads having a relatively small diameter partially embedded or in contact with a reflecting surface. The reflector described and shown therein is so constructed that a light beam including rays parallel to or forming a relatively small angle with the axis of the reflex reflecting surface can be effectively reflected back.
A "reflex" light reflector (the term "reflex" reflector having been made use of to distinguish it from mirrors which cause specular reflection, and from diffusing surfaces which do not ensure selective return of the light in the direction of incidence), which also includes the above arrangement of spherical short focus lenses and beads including reflex reflecting means, has been described in the U.S. Pat. No. 2,294,930. The behaviour of such reflex reflecting systems has been extensively analyzed in said latter patent literature, where there has been described and illustrated how the "brilliancy" (this term signifies the intrinsic efficiency of reflex reflectivity) drops as the angle of incidence (i) increases, and how it is nearly zero for angles (i) of 40.degree. or higher.
While such and other reflex reflecting systems might be assumed to be generally efficient, they have been proven as not successful when partially embedded in a nearly planar and horizontal surface, such as that of a sign formed on or applied to a traffic carrying surface, while they are efficient when so associated with sharply bulging markers that the exposed portions of their lenses are facing the source of light, that is are impinged by light rays under a small angle of incidence.
As a consequence of the above summary (the applicant acknowledges that only a part of the wide literature has been indicated hereinabove) it is evident that the current technology of reflex reflecting systems and structures fails to provide systems of the above character which can efficiently provide a desirable brillancy under grazing light, when the part-spherical exposed portions of their lenses bulges up, for a distance corresponding to a portion of their radii only, from a nearly planar and horizontal non-transparent surface, and when impinged at their top portions by grazing light. In other words, the prior art systems cannot be efficiently made use of for imparting favorable nighttime visibility to traffic regulating signs which form part of a traffic carrying surface.
It is therefore the object of this invention to provide a new and improved reflex-reflecting system of the character referred to above, adapted to be principally but not exclusively made use of for imparting a substantial and uniform brilliancy and consequently visibility, to the surface of traffic regulating signs formed on a traffic carrying surface, by embedding a plurality of such systems in the sign forming compound which spacing by scattering.